1. Field of the Invention
This invention relates generally to vehicle windshield wipers and, more particularly, to a new and improved windshield wiper transmission effecting an advantageous combination of wiper arm drive torque and wiper arm speed.
2. Description of the Prior Art
In most automotive windshield wiper systems, blade carrying wiper arms oscillate across the windshield in arcs of varying dimension about pivot axes adjacent the windshield. Since the arms reverse direction at inner and outer wipe limits, minimum noise and inertia loading are achieved by reducing the angular velocity of the arms as they approach the wipe limits. Conversely, to reduce the duration of each wipe cycle, it is desirable to maximize the angular velocity of the arms. In addition, where ice and snow may be encountered, maximum drive torque at the wipe limits and during initial movement from parked positions of the wiper arms is desirable. In the past, mechanical linkage systems between the arms and a single drive motor have fulfilled some or all of these requirements but at the expense of economy and efficient use of vehicle space. In some recent windshield wiper system proposals separate drive motors and transmissions are provided for each wiper arm with electronic control provided to effect motor reversal at the wipe limits and, in some cases, to even increase the wiping arc when a wider pattern is desired. In these systems, however, the torque mutiplication ratio of the gear transmissions between the motors and the wiper arms is constant so that only by manipulating the motors themselves can variable wiper arm torque and speed be achieved. Finally, another system has been proposed wherein a non-arcuate wiping pattern is achieved through a complicated gear and rotating case arrangement. In this proposed system, uniform wiper blade speed throughout the non-arcuate motion path is achieved with a gear train having a plurality of eccentrically mounted circular gears. A windshield wiper system as disclosed herein represents an improvement over these and other known systems in that it includes a transmission according to this invention which produces a particularly advantageous combination of wiper arm drive torque and angular velocity in a simple and economical structure.